IP packet traffic is increasing with the rapid growth of the Internet. Also, penetration of the portable telephone service causes a growing demand to standardize and implement IMT-2000 (International Mobile Telecommunications 2000). With such a background, high-speed IP communication in the mobile environment will become in more widespread use.
The IP communication in the mobile environment requires IPv6 (Internet Protocol version 6) because there is a problem of possible exhaustion of IP addresses in the conventional IPv4. In the IPv6 environment, it is mandatory that IP Sec/IKE (IP security/Internet Key Exchange) be employed in terminal units including servers. By employing IP Sec, secure communication service may be obtained.
However, according to IP Sec/IKE, it is necessary to install a key exchange server (IKE server) in the terminals. This requires the terminal to have a relatively high speed processing unit (CPU, etc.) as well as a large capacity memory, because complicated processing is needed in such a key exchange server.
For this reason, though it is easy to introduce IP Sec/IKE in the terminal such as a personal computer and a server, there may be a problem to implement IP Sec/IKE in portable terminal devices such as a portable telephone and a portable digital assistant (PDA), in which miniaturized and light structure is demanded.
There has been devised a Diffie-Hellman method to enable a key exchange function in an ordinary communication path in which secure communication is not guaranteed. However, in order to incorporate this method, calculation of a power has to be done in each terminal requiring key exchange. This consumes a lot of resources in the terminal, and imposes substantially large load on such a portable terminal device.
Moreover, considerably large electric power is consumed in performing the IPSec/IKE processing. Therefore, it is not a practical solution to install IP Sec/IKE in the portable terminal device also from the viewpoint of power consumption. Accordingly, it has been needed to incorporate a service based on IP Sec/IKE with minimized functional addition into such a portable terminal device.
For the above-mentioned reason, there has been devised a key exchange processing technique to be performed in other equipment than a portable terminal device, functioning as proxy for the portable terminal device. A technique has been disclosed by use of a home server accessed by a user terminal device, performing as proxy for the terminal device. (For example, refer to the following patent document 1.)